Conventional microwave components such as waveguides and resonant cavities can provide only limited coupling of incident microwave energy into samples for irradiation. In the Thibault U.S. Pat. No. 3,599,120 a double ended helix waveguide transmission structure is provided in an effort to achieve more efficient coupling of microwave energy from a resonant cavity into a sample. The spiral helix structure at one end is inserted in the resonant cavity of a microwave energy source to pick up microwave frequency electromagnetic energy. The energy is transmitted along a conductive stem to the second spiral helix structure at the other end of the stem outside the resonant cavity. The second spiral helix structure is immersed in the sample, such as a liquid sample, for radiating energy into the sample. The purpose of the Thibault structure is to excite electron spin resonance in the sample material for microwave spectroscopy measurements on the sample material.
A difficulty in attempting to apply the Thibault structure to irradiation of biological samples is that the integrity of the sample is lost upon immersion or invasion of the spiral helix into the sample. There is no provision for maintaining the integrity of the sample in sealed standard sample tubes. Another disadvantage is that only one sample at a time can be irradiated using the relatively expensive Thibault equipment.
Similarly in the Jean U.S. Pat. No. 4,221,948, microwave antenna structures are embedded in a cylindrical receptacle containing the dielectric material to be treated with microwave energy. The Jean structure is referred to as an "applicator" for treating dielectric materials. Embedded antennas may be cylindrical, slotted, and helical, etc.
Another problem arises in the assessment of effects of microwave energy irradiation on biological and biochemical samples. It is desirable to separate and delineate effects causes by direct absorption of the microwave energy in target tissues and molecules from the indirect effects causes by heating of surrounding water molecules, etc. The Gray U.S. Pat. No. 3,494,723 describes temperature control using a circulating coolant gas in a microwave energy system. However, the Gray system is a heat sterilization or pasteurization system using heat treatment. The coolant system is intended only for controlling the temperature level of treatment and for rapid cooling after treatment. No references of which applicant is aware are specifically directed to the problem of separating and delineating direct microwave energy absorption effects from indirect heating effects.
The general field of microwave radiation contains a substantial literature on microwave antenna structures for transmitting and receiving microwave frequency electromagnetic radiation in space. For example the Cone et.al. U.S. Pat. No. 4,014,028 describes a backfire bifilar helical antenna for radiating and receiving circularly polarized waves in a backfire mode. There is no teaching however how such microwave transmitting and receiving structures might be applied to the field of irradiating biological samples nor is there any suggestion in this general literature of the desirability of doing so. Another problem associated with conventional microwave transmission and receiving antenna structures is that the radiation field may extend into the surrounding environment with unknown effects on workers in the vicinity.